Is Quick Drying Cement Safe ?

[phil_ip]

I'm making a DIY backround. Is it safe to use quick drying cement to create the backround. If I did I would place the backround in the tank, let it sit in there with water, but no fish, for about two months, doing 50% water changes every week. Then after the two months introduce the fish. Do you think this would be safe to do?

[Skittyfish]

Where I am from most quickcrete has some type of limestone in it, which wouldn't be good for your fish.

[morleyz]

I think it would be perfectly harmless...I've seen many ponds and even a couple of tanks made from concrete...if anything did leech, it might just raise your KH a little.

[Darkangel]

I would be very hesitant to try this. Concretes will leach chemicals and compounds into water. Those concrete ponds that you see have been cured or weathered.

[pinballqueen]

Also, cement tends to expand a little before it starts shrinking, so you run the risk of cracking your tank. It will get very hot during the drying process as well, which might damage the seals. (This applies to cement and concrete mixes that contain plaster of paris as the main fixative...) Cement takes literally years to cure fully, as the center takes much longer than the outer crust. This is why cement and concrete driveways develop cracks. The outer layer is cured, but the inside is still slightly pliable. It will never fully dry underwater without chemical additives (concrete used in bridge construction is preformed months ahead of time and reinforced with steel for this reason.)

If you were to try something like this, you might try the cement they use to repair cracks in swimming pools, but once again, you will be plagued with chemical imbalances for a very long time (something you don't have to worry about for a swimming pool).

Wish I had some better advice....:(

[Matak]

When I first got into this hobby, I used mortar (brick cement) to peice rocks together. It nearly killed my fish. I've since learned and realize that what darkangel & the others have said is correct. However, it would be safe to use cement in your tank if you apply a few coats of potable water epoxy on the cement. Give the cement at least 7 days to cure and give the epoxy the same period of time, both at room tempurature.

HTH

[slipknottin]

concrete raises the Ph.

[pinballqueen]

Maybe if you have a pottery studio nearby, you could sculpt the deco from ceramic clay and have it fired and glazed. The same stuff they sell at the lfs.... It would cost a little, but you'd get exactly what you're wanting.... then you can just use silicone to adhere the deco piece to the back of your tank.

[superstein61]

Well, I agree with most of the above - let me just add:

First - as noted, concrete will raise your ph. So unless this is a cichlid tank, you may have some problems.

Second, there is a way to cure the concrete - I read it in the DIY background instructions a couple folks did on a cichlid site (I can't recall the name / link right now). That will make it safe for fish - but again, your ph will be affected ( I seem to recall them curing it by soaking in slatwater - but I could be wrong)

third - why don't you instead go with epoxy resin and sand? thats what I did - the resin is inert - and the sand gives a textured finish just like rocks - check out my pics / instructions on the Tank Pic link below

[morleyz]

Well if concrete is so chemically dangerous to your fish, you guys might want to let the guys over at GARF know...cause they're making live rock out of it.

[slipknottin]

They let the concrete rock cure in a bucket of SW for at least 2 months before adding it to a tank. Otherwise it will raise the Ph quite high.

[phil_ip]

Where can you buy epoxy resin, I've checked everywhere, is there an alternative to it ?

[phil_ip]

The chemical used in the cement I would use is called polymer, someone already said this was safe because it is hydrocarbon chains fused tightly together to form a chemical bond, and that plastic of all types are made of polymer, he or she also said polymer is impervious to water and will not release any bad molecules into the water. Thanks IGKYA!!!, but what do the rest of u think ?

[morleyz]

Originally posted by slipknottin
They let the concrete rock cure in a bucket of SW for at least 2 months before adding it to a tank. Otherwise it will raise the Ph quite high.

Ok...agreed, but I don't know where people are getting this "toxicity" concept from...

[slipknottin]

I dont know either. Ive used concrete in both African cichlid, CA cichlid and SW tanks with no problems.

[carpguy]

Phil_ip,
You should be able to find epoxy resin at the Home Depot, Lowes, etc. — look in the paint section.

The descriptions I've read of people using cement to make features usually include some kind of underlying form with a cement shell over top sealed with epoxy. Should take care of curing issues as well as pH issues.

[superstein61]

Phil-ip - I would also check Home Depot or Lowes - but they didn't carry epoxy resin in my area.

I used Epoxy resin from West Systems. Most woodworking stores carry this or similiar brands. You can search for their US dealers at:

http://www.westsystem.com/frames/tier2/productinfo/usdealers.htm

they also have dealers on their site that will ship the product to you

[Stias']

Originally posted by pinballqueen
Also, cement tends to expand a little before it starts shrinking, so you run the risk of cracking your tank. It will get very hot during the drying process as well, which might damage the seals. (This applies to cement and concrete mixes that contain plaster of paris as the main fixative...) Cement takes literally years to cure fully, as the center takes much longer than the outer crust. This is why cement and concrete driveways develop cracks. The outer layer is cured, but the inside is still slightly pliable. It will never fully dry underwater without chemical additives (concrete used in bridge construction is preformed months ahead of time and reinforced with steel for this reason.)

If you were to try something like this, you might try the cement they use to repair cracks in swimming pools, but once again, you will be plagued with chemical imbalances for a very long time (something you don't have to worry about for a swimming pool).

Wish I had some better advice....:(

I can only hope you are joking, its just not true...

Stias'

[slipknottin]

Originally posted by Stias'


I can only hope you are joking, its just not true...

Stias'

Whats not true?

[carpguy]

While most of what PBQ wrote is true, most of it also doesn't really apply to the quantities we're talking about here.

Large thicknesses and quantities do take months or even years to fully cure. A quarter of an inch skin will not take nearly as long. Nor will it generate that much heat. Keeping concrete wet during curing is an important step in avoiding cracks, but I'm not sure if underwater is what they meant.

And the steel rebar is in bridges (and buildings) to add tensile strength, not to help support it during curing. Steel has incredibly good tensile strength, and little compressive strength, concrete just the opposite. Steel-reinforced concrete has both.

[slipknottin]

Concrete does expand when curing also, and it can bust through a tank.

[pinballqueen]

I learned about the awesome expansion power of plaster and cement when trying to make plaster casts for an art project...

The mold burst the container it was in, ruining a perfectly good casting, burning the subject's skin in the process (it was a hand, guys, let's keep it clean, shall we?).... I had to start all over....

Many forms of cement and concrete contain plaster of paris, and therefore the risk is definitely there for all of the problems I presented if one of these varieties is used.

It's not so much of a problem of the cement/plaster/concrete poisoning your fish as it is a problem of altering your ph and/or breaking your tank...

[Glenstorm]

Epoxy resin is also available at boating stores. Boating stores also offer fillers for the resin that can make it more like putty and add color to your project. For sculpting fillers, look for something called microballoons. They are more less miniscule balloons made out of synthetic materials. They look like a powder but are actually very small spheres. I have this around to repair my boat.

I am contemplating making a background out of this and some sort of wire frame. . . either chicken wire or hangers. I figure that I won't have to worry about corrosion since the wire will be encased in the resin. . .

Dan

[Stias']

Originally posted by slipknottin


Whats not true?

Just about everything so due to the length of this post I am gonna do it as quick as I can, if you got a specific question ask away.

The following are from PBQ's first post, the one in which I was hopeing she was joking...
Also, cement tends to expand a little before it starts shrinking, so you run the risk of cracking your tank. True but somewhat misleading. It does expand a little (VERY little) then shrinks. It will not expand once it startes its "initional set", this is the point when it showes signs of hardening but if you run your finger through the cement, it still is free moving. We are talking 10 minutes after mixing then we are in shrink mode. Nobody can work that fast to assemble than break a tank due to expantion, if you can, PM me and I have a job for you and will hire you tomarrow.

It will get very hot during the drying process as well, which might damage the seals.I think this rumor started right about the time the Bolder dam was built (since renamed the Hover dam). It will only have that kind of heat if you are talking a large amounts. A basement pour would be lucky to get a degree or three warmer that the ambeint temp. (unless in sun ect.). That is also assuming they didnt add anything to speed it up as is done in the winter to help prevent freezing or to speed up the cure but we are not talking adding special aditives. Even with chemicals, it aint gonna get hot enough to damage the silicone, you probally couldnt even feel the difference between the crete and some other object the room.

(This applies to cement and concrete mixes that contain plaster of paris as the main fixative...) concrete and mortar does not contain plaster of paris, they contain portland cement. Mortar probally contains less than 25% portland and concrete 20% portalnd or less.

Cement takes literally years to cure fully, as the center takes much longer than the outer crust. concrete CAN cure for years after being poured but that is not to say it DOES take years. Industry standard in 28 days to be called "cured" or "fully cured". If you seal it, you can drive a truck on it in a week. Just because the outside seems harder than the inside after pouring concrete, say, 2-4 hours later means nothing, the outside is just dry, not cured. They are 2 different things.

This is why cement and concrete driveways develop cracks.Driveways develop cracks because it SHRINKS, not because the inside is soft like a cream filled doughnut. The cracks are called stress cracks so masons put in that little groove you see in sidewalks to encourace the concrete to crack where you want it, rather than anywhere it happens to want to. Adding control joints is as much as art as a science and if a crack is seen where it is unexpected, grab the soft cut saw and make one. It is kinda like when you get a little crack in your winshield in your car, you dont want it going up into your vision so you turn on the defroster and grab some ice and try to work the crack where you can live with it (where it dont go into your vivion or the cops make you replace the winshield)

The outer layer is cured, but the inside is still slightly pliable.No, I explained it above. If you see (or feel more accurately described) concrete that is hard on the outside and softer on the inside, it is DRY, not cured. Use a sealer or wet it down with water to keep it from drying out. This also helps prevent a few initional stress cracks that wont amount to anything (will remain small).

It will never fully dry underwater without chemical additivesNot true, concrete can and is poured underwater all the time. To test this, flag down a concrete truck or find one where they are building. Take a 5 gallon pail, put 3 gallons of concrete in it and then cover with 1.5 gallons of water. You have an underwater pour now, we know the plastic pail will not let it "dry" from the sides or bottom and the top is under water. Let sit for a week, dump out the water and try to get out the ramaining concrete (without a hammer). Good luck with that.

(concrete used in bridge construction is preformed months ahead of time and reinforced with steel for this reason.)Steel in in concrete for strength, not because it is a bridge. Add straw to mud and it adds strength, same with steel in concrete. Steel is used in almost every pour of concrete but fiber mesh is becoming popular because of the reduced labor. Fiber mesh is like ground up fiberglass (well, it is that) and it acts the same way as steel which is the same as adding straw to mud, it adds strength.

If you were to try something like this, you might try the cement they use to repair cracks in swimming pools, but once again, you will be plagued with chemical imbalances for a very long time (something you don't have to worry about for a swimming pool).Now this stuff is specially made to NOT shrink, in fact a little expantion is good with it to help fill the crack. I know the stuff you use on a leaky basement is like that and I believe the stuff for swiming pools is the same, just a much higher price tag. If you can afford a pool, you can afford to pay.

carpguy said... "While most of what PBQ wrote is true, most of it also doesn't really apply to the quantities we're talking about here.

Large thicknesses and quantities do take months or even years to fully cure. A quarter of an inch skin will not take nearly as long. Nor will it generate that much heat. Keeping concrete wet during curing is an important step in avoiding cracks, but I'm not sure if underwater is what they meant.

And the steel rebar is in bridges (and buildings) to add tensile strength, not to help support it during curing. Steel has incredibly good tensile strength, and little compressive strength, concrete just the opposite. Steel-reinforced concrete has both. " That is pretty much right on but I do want to comment that even in large pours, a month is concidered cured. We are talking 95% or better cured. It is cheaper to enginer more concrete if you are worried about the little 5%. In other words, by a month, just call it full strength and be done with it, but yes, concrete CAN cure for years under ideal conditions.

slipknottin said "Concrete does expand when curing also, and it can bust through a tank. "No, I explained it already, see above. By the time you start putting bricks, block, stone, buildings, whatever, or even rocks in a tank, its done expanding and shrinking. If someone is willing to sacrifice a big tank to test it, I will fill it and show that if it is strong enough to hold water, it can (probally) be filled to the brim and not bust the tank. Anybody want to try it, contact me.

pinballqueen said "I learned about the awesome expansion power of plaster and cement when trying to make plaster casts for an art project...

The mold burst the container it was in, ruining a perfectly good casting, burning the subject's skin in the process (it was a hand, guys, let's keep it clean, shall we?).... I had to start all over....Plaster of paris is a whole different cat, I just looked up the MSDS on google and found it to be 95% calcium sulfate and only 5% silica (read sand) That causes the the heat up effect to be high and the shrinkage to (I think) be high also. Plaster of paris and portland are not the same...



***Ok everybody, that became quite a book, sorry but there were alot of things to cover. I hope nobody takes offence to the corrections I made, I dont mean them personal, just correcting with facts. I would also like to say I have no idea how mortor or concrete would affect KH Ph or anything like that or how the chemicals in epoxies would affect the fish, thats just not my area of study/work. I hope this cleared things up, if not, just post specificly what ya need explained.

Stias'

Oh, yes you can get a nasty burn with concrete but it is a chemical burn, not a heat type burn. Some people are more suspital to this than others, in fact I worked with a guy that had to wear a new pair of gloves every day due to his easy burns which looked like a rash to me. Loved working by him, got a set of 1 day old gloves everyday.